function objToSearchString(obj) {
    str = ``
    //进行遍历
    for (var key in obj) {
        str += `${key}=${obj[key]}&`
    }
    return str.slice(0, str.length - 1)
}

//封装ajax函数
function ajax(method, url, params) {
    return new Promise((resolve, reject) => {
        var xhr = new XMLHttpRequest()
        xhr.open(method, method == 'get' ? url + '?' + objToSearchString(params) : url)
        xhr.onreadystatechange = function () {
            if (xhr.readyState == 4) {
                resolve(JSON.parse(xhr.responseTextn))
            }
        }
        xhr.setRequestHeader('content-type', 'application/x-www-form-urlencoded');
        xhr.send(method=='get'?null:objToSearchString(params))
    })

}